Improve definition of XExpr type (#1444)

add Pcdata to definition of XExpr type

Author: joergen7

typed-racket-more/typed/xml.rkt

@@ -13,7 +13,7 @@
   (U Comment P-I))
 
 (define-type XExpr
-  (U XML-Misc Cdata Positive-Index
+  (U XML-Misc Cdata Pcdata Positive-Index
      Number String Symbol
      (Pair Symbol (Pair (Listof XExpr-Attribute) (Listof XExpr)))
      (Pair Symbol (Listof XExpr))))